An expanded grid (i.e., a net-like grid) obtained by forming slits in, for example, a zigzag manner on a lead alloy sheet, followed by expanding, has been conventionally used as a grid for use in a storage battery, as disclosed in JP-A-7-320743. The expanded grid includes, an upper frame having a lug portion formed thereat, a lower frame opposed to the upper frame, and a net-like frame formed between the upper frame and the lower frame. A space defined by the upper frame, the lower frame, and the netlike frame is filled with an active material, thereby constituting an electrode plate.
However, the expanded grid has no frame bone for connecting the upper frame and the lower frame to each other on right and left sides, and therefore, is liable to be elongated in a vertical direction, thereby raising a problem that short-circuiting is liable to occur. The expanded grid, does not have a frame bone, and therefore, the net-like frame between the upper and lower frames is serrate from the upper frame to the lower frame. Consequently, a current channel up to the lower frame from the lug portion becomes long, thereby increasing an electric resistance. Consequently, a potential distribution becomes uneven over the entire electrode plate, thereby raising problems of local corrosion and a short lifetime of the electrode plate.
In the meantime, a grid including, inside of a square frame bone, many lateral frames parallel to each other and many radial frames radially extending from a lug portion disposed on an upper side portion of the frame bone is conceived as a grid for use in a storage battery, as disclosed in JP-Y-8-2921. The radial frames are formed with branch frames. Each of the branch frames includes: a branch starting frame extending sideways at a large angle with respect to the base of the radial frame and a bent starting frame continuous to the branch starting frame and bent in a radial direction.
However, the grid includes a portion that is apart from the lug portion (in particular, the branch starting frame) on a channel from a lower section toward an upper section along the branch frame, and therefore, a current channel up to the lug portion becomes long, thereby increasing a current pathway, resulting in an increase in electric resistance. Consequently, a potential distribution becomes uneven over the entire electrode plate, thereby raising problems of local corrosion and a short lifetime of the electrode plate.